Grain-oriented electrical steel sheets are material mainly used as the iron core of a transformer. From the perspective of achieving high efficiency of a transformer and reducing the noise thereof, a grain-oriented electrical steel sheet is required to have material properties including low iron loss and low magnetic strain.
In this regard, it is important to highly accord secondary recrystallized grains of a steel sheet with (110)[001] orientation, i.e. the “Goss orientation”. It is known that if the degree of orientation of the crystal grains is too high, however, the iron loss ends up increasing. Therefore, to solve this problem, a technique has been developed to introduce strain and grooves into the surface of a steel sheet to subdivide the width of a magnetic domain to reduce iron loss, i.e. a magnetic domain refining technique.
For example, JP S57-2252 B2 (PTL 1) proposes a technique of irradiating a steel sheet as a finished product with a laser to introduce linear high-dislocation density regions into a surface layer of the steel sheet, thereby narrowing magnetic domain widths and reducing iron loss of the steel sheet.
Furthermore, JP H6-072266 B2 (PTL 2) proposes a technique for controlling the magnetic domain width by means of electron beam irradiation. By this method of reducing iron loss with electron beam irradiation, electron beam scanning can be performed at a high rate by controlling magnetic fields. Since there is no mechanically movable part as found in an optical scanning mechanism used in laser application, this method is particularly advantageous when irradiating a series of wide strips, each having a width of 1 m or more, continuously and at a high rate to apply strain.